Preliminary data this past year show that parathyroid hormone (PTH) is important for buffering acute acid loads. Normal nephrectomized rats will be acutely administered HCl, 10mM/kg body weight, and distribution of the acid between extracellular and cellular buffers calculated. Extracellular buffering will be determined by measuring the change in extracellular bicarbonate using 36chloride to measure the extracellular space. Intracellular buffering will be considered equal to the increase in extracellular sodium and potassium. In addition, the intracellular pH of heart, liver, and skeletal muscle will be determined on biopsy specimens taken at the end of the experiments using a triple isotope technique in which C14-DMO distribution is the measure of cell pH. Similar experiments will be performed in two other groups of nephrectomized rats. The first group will have been parathyroidectomized 24 hours before the experiment. The second group will also be parathyroidectomized but two hours before receiving the acid load this group will receive 10 units/kg body weight of synthetic PTH. Acid distribution and cell pH values will be compared in the three groups of animals. Similar studies are planned for dogs in order to overcome certain technical problems and to demonstrate that the effect is not species specific.